The invention relates to a low voltage switchgear for a certain nominal current, in particular in alternating voltage systems, with a single or multipole contact system with a corresponding number of fixed contacts and movable contacts, a magnet armature that moves movable contacts, at least one magnet coil energized by direct current and a setpoint switch release. More particularly to such a switchgear in which the magnet armature operates in a bistable way, namely by brief direct current energizing of the magnet coil released by the setpoint switch release with one of two possible conduction directions, so that it can be brought into one of two switching positions, namely a switching-on or a switching-off position, and remains in the respectively reached switching position.
The known low voltage switchgear, on which the invention is based (published German application DE-A 3 940 242), is suitable for low voltages in the range of 110 volts, 220 volts, 380 volts, and depending on how it is equipped, can switch nominal currents from several amperes up to 20 A and more. When this low voltage switchgear is equipped with a corresponding arc-quenching device at the contact system, higher currents can also be switched.
The known low voltage switchgear is suitable especially for switching multipole contact systems, for example, all three phases of a three-phase alternating voltage network. The movable contacts of the contact system, here, are moved by magnet armatures that are moved by one or two magnet coils which, for their part, are energized primarily by direct current. The magnet armature is made as a permanent magnet armature consisting of one or more permanent magnets with identical or opposite poles. In various embodiments, monostable or bistable solutions with one or two magnet coils and one or two permanent magnets in the magnet armature are described for this low voltage switchgear. There, it is explained in detail how the magnet armature can be kept in one of two switching positions, in each case, by the action of the permanent magnets. As an alternative to positioning by magnetic force, a latching positioning by mechanical elements is also described It is also described that a magnet yoke in cup form can be associated with the magnet armature to increase the switching speed of the switchgear.
In the low voltage switchgear known from the prior art on which the invention is based, the movable contacts are made as contact bridges that each short-circuit two associated fixed contacts. This does not mean, in the framework of the teaching of the invention, that the movable contacts could not also be made as contact levers that open on one side or the like. Basically, the movable contacts of the contact system could also be moved, not only by the magnet armature but, with a stationary magnet armature, also by a movable magnet coil. However, in practice this is the exception and consequently, is not explained below in more detail. In any case, this kinematic reversal belongs to the teaching of the invention.
In the low voltage switchgear known from the prior art that was explained above, nothing has been said about the control of the magnet coil or magnet coils. From other prior art, it is known to provide low voltage switchgears of the type being discussed, for example, with overcurrent releases (published German application DE-A 3 304 921).
In general, basically, this type of low voltage switchgear previously was divided into various switchgear groups. First, there are known low-voltage fuse switch-disconnectors and low-voltage fuse switches in which fuse links are used to protect against overload current and short-circuit current. A corresponding characteristic curve with switching time depending on the magnitude of the flowing current with respect to disconnection guarantees that no damage can be done. But, after each release of the overload and short-circuit protection, the fuse link must be replaced. Switching on and off is performed as a rule by hand, remote operation is not provided. Since, for example, in a three-phase network, only the fuse link can respond to a switched phase, in some cases, for example, to avoid two-phase operation of a connected three-phase alternating current motor, additional monitoring must be provided. Finally, there exists the danger of switching on when there is a short circuit, in which case the switching-on speed depends on hand operation.
As low voltage switchgears suitable for relatively high nominal currents, contactors are extremely well suited for high numbers of operations. However, suitable fuses would have to be connected upstream from a contactor for overcurrents and short-circuit currents. Mechanical disconnection of a started contactor is not possible, by the way, since the contactor solenoid must be energized during the switching-on period.
Finally, low-voltage circuit breakers are known in which a release for overcurrent and short-circuit current is regularly provided. However, this is performed mechanically by a lock that releases tripping springs. Sometimes metallic preliminary interruptors are allocated that cause an interruption of the circuit after a short time, and thus, guarantee a limitation of the short-circuit current (not reaching the peak value of the current), before the contact system is completely opened by the lock. High numbers of operations usually cannot be achieved with circuit breakers as they can with a contactor.